Galling thrips on Australian Acacia

Current evidence suggests that the entire suite of Phlaeothripinae on
Australian Acacia species comprises a
single lineage that has radiated subsequent to a single invasion of the
genus Acacia. [Morris DC, Schwarz
MP, Cooper SJB & Mound LA, 2002. Phylogenetics of Australian Acacia
thrips: the evolution of behaviour and ecology. Molecular Phylogenetics
and Evolution 25: 278-292], [Crespi
BJ, Morris DC & Mound LA, 2004. Evolution of ecological and
behavioural diversity: Australian Acacia thrips as model organisms.
Australian Biological Resources Study & Australian National Insect
Collection, CSIRO, Canberra, Australia. 328pp].

Acacia oswaldi
galls

The radiation appears to have been driven primarily by competition for
small enclosed spaces that provide protection from insolation and dehydration
in the extremely arid environment of central Australia, but also by the
need for protection from the many and abundant ant species [Crespi BJ
& Mound LA, 1997. Ecology and evolution of social behaviour among
Australian gall thrips and their allies. pp. 166-180. In Choe, J. &
Crespi, BJ (eds) Evolution of Social Behaviour in Insects and Arachnids.
Cambridge University Press.]

More than 25 species of Phlaeothripinae on Acacia are known to
induce galls. In some of these gall-inducing thrips the first generation
produced by the winged gall-foundress is small and the adults develop
as wingless 'soldiers' [Kranz BD, Schwarz MP, Wills TE, Chapman TW, Morris
DC & Crespi BJ. 2001. A fully reproductive fighting morph in a soldier
clade of gall-inducing thrips. Behavioural Ecology and Sociobiology50:151-161].

These wingless individuals defend the gall from
invasion in some species, particularly from the kleptoparasitic Koptothrips
species, but in other members of the same genus there is little evidence
of defensive behaviour [Perry SP, McLeish MJ, Schwarz MP, Boyette AH, Zammit
J and Chapman TW. 2002. Variation in propensity to defend by reproductive
gall morphs in two species of gall-forming thrips. Insectes Sociaux49: 54-58]. The second generation within these galls is of fully
winged adults that disperse and induce further galls (eg. Oncothrips
morrisi).

Acacia pendula galls

In contrast, in several other species
of the same genus of thrips, the gall-foundress becomes physogastric and
produces a single generation (eg. Kladothrips rugosus), and in some
species this may comprise as many as 1000 individuals.

Winged foundress of
Oncothrips morrisi

Kleptoparasitic thrips of the genus Koptothrips invade the galls
of many Kladothrips species.

These invading thrips kill the original gall thrips by stabbing with
their fore tarsal teeth, and then breed for one or more generations in
the galls that they have usurped, sometimes producing large populations.
Although kleptoparasites, these thrips are phytophagous not predatory.

Wingless female soldier
of Oncothrips morrisi

Two further suites of phlaeothripines on Acacia are the domicile
creating species and the opportunist
species.